The ability to quantitatively measure tear production is important for the diagnosis of many types of lacrimal dysfunction. Patients may experience either excessive tear formation (epiphora) or decreased tear production, such as keratoconjunctivitis sicca (associated with Sjogren syndrome). The measurement of tear production levels is also important for determining if a patient is a good candidate for contact lenses.
Quantitative measurement of tear production has traditionally been measured by a Schirmer I Tear Test. The standardized Schirmer I Tear Test consists of a 5.times.35 mm strip of Whatman #41 filter paper; the paper has a notch located 5 mm from one end of the strip. The notched end of the strip is rounded.
The Schirmer Tear Test is performed as follows. The test strip is bent at the notch (.about.120.degree. bend). The rounded end of the Schirmer I Tear Test strip is then inserted into the lower conjunctival sac of each eye. The eyes are then closed. The strip is progressively wetted by capillary action drawing up tears as they are produced. The distance the tear migration front has moved is measured after 5 minutes. The migration distance of the tears is measured from the notch of the strip as the zero point. Reading the test involves removing the strip from the eye and placing it against a scale graduated in millimeters. 15 mm of wetting in 5 minutes is considered normal. It is imperative that the tear migration front be measured as close to the 5 minute time mark as possible because the tear front will continue to migrate up the strip after the strip is removed from the eye. Thus, late readings give rise to results that are artificially high.